The present disclosure relates to an electrophotographical image forming apparatus.
As an electrophotographical image forming apparatus, there is known a printer which includes photosensitive elements for carrying developer images, and transfer members for transferring the developer images formed on the photosensitive elements onto a paper sheet.
For example, there has been proposed a color printer which includes four photosensitive drums that are provided corresponding to colors of black, yellow, magenta, and cyan, respectively, a conveyor belt that conveys paper sheets so that the paper sheets come into contact with all photosensitive drums, and four transfer rollers that are provided corresponding to the four photosensitive drums, respectively, so that the conveyor belt is interposed between the transfer rollers and corresponding photosensitive drums.
In this color printer, a resistance value between the most upstream photosensitive drum and a transfer roller facing the corresponding photosensitive drum is measured, and a target value for an electric current to flow between the photosensitive drum and the transfer roller (a transfer current target value) is set based on a resistance value before a paper sheet is conveyed and a resistance value when a paper sheet is being conveyed.
Then, a voltage to be applied between the photosensitive drum and the transfer roller is controlled such that the electric charge to flow between the photosensitive drum and the transfer roller approximates to the transfer current target value.